The present invention generally relates to processes for preparing extruded foam products and more particularly to a process for producing such products wherein surface defects are minimized.
Extruded synthetic resinous foams are useful materials for many applications including thermal insulation, decorative purposes, packaging and the like. Because of the manufacturing process, extruded foams have surface defects marring their appearance. These defects often produce a rippled or pebbled surface. It is desirable to reduce these defects and improve the surface appearance of these boards.
There has been a movement to replace conventional halo-carbon blowing agents in favor of purportedly more environmentally safe halo-carbon free blowing agents such as carbon dioxide, nitrogen, argon, water, air, nitrogen, and helium. However, these halo-carbon free blowing agents, in particular carbon dioxide, have higher foaming rates and higher volatility leading to greater surface defects in the extruded foam.
It would be desirable to discover an additive to the extruded foam manufacturing process that both reduces or eliminates surface defects when halo-carbon free blowing agents are used.
The present invention employs polyethylene wax to reduce or eliminate the occurrence of surface defects where halo-carbon free blowing agents are employed in an extruded foam manufacture process. Polyethylene wax has been reported to increase cell sizes when in an extruded foam manufacture process employing halo-carbon blowing agents (EP 0 427 533 B1), but it has now been discovered surprisingly that addition of polyethylene wax in an extruded foam manufacture process reduces or eliminates the occurrence of surface defects in the final product when halo-carbon free blowing agents are employed.
The polyethylene wax containing extruded foam products of this invention are characterized by a generally smooth substantially defect free surface and contain a majority of closed cells which are free of any trapped halo-carbon blowing agents.